Three-phase heating element

ABSTRACT

A silicon carbide, three-phase heating element having a hollow, generally cylindrical body formed with three circumferentially spaced legs comprising the cold end section and three spaced, parallel spirals constituting the hot zone section and terminating in a common juncture. The slots between the spirals can be filled with a ceramic insulating material.

United States Patent [191 111] 3,859,501 Matys 1 Jan. 7, 1975 [541 THREE-PHASE HEATING ELEMENT 3,360,760 12/1967 [75] Inventor: Stanley J. Matys, Depew, N.Y. 3 A z I 3,467,812 9/1969 [7 ssIgnee inscqulalgidcitfreiliilent Company 3,518,351 M 3,688,007 8/1972 McKenna et al. 13/20 [22] Sept 1973 FOREIGN PATENTS OR APPLICATIONS 1 1 PP 398,186 310,066 12/1955 Switzerland 13/25 594,530 6/1959 ltaly 13/25 [52] U.S. Cl 219/553, 1 3/25, 219/541,

317 93 33 299 333 330 Primary ExaminerVolodymyr Y. Mayewsky 51 Int. (:1. H05b 3/10 Attorney, Agent, or FirmChristel & Bean [58] Field of Search 13/20, 22, 25, 31;

219/260, 270, 541, 552, 553; 317/98; [57] ABSTRACT 338/269 333 A silicon carbide, three-phase heating element having a hollow, generally cylindrical body formed with three [56] References cued circumferentially spaced legs comprising the cold end UNITED STATES PATENTS section and three spaced, parallel spirals constituting 1,450,725 4/1923 Hodson 338/269 the hot zone section and terminating in a common 1,933,123 10/1933 gfl d---- X juncture. The slots between the spirals can be filled 2,556,679 6/1951 C zcpek 338/296 with a ceramic insulating materiaL 3,057,936 10/1962 HIll 13/25 3,336,431 8/1967 Biddulph 13/25 6 Claims, 6 Drawing Figures ment.

I installed and replacedduring furnace THREE-PHASE HEATJNG ELEMENT BACKGROUND OFVTHEY INVENTION anda high resistanceportioi t. The high resistance portions are connected to a Qfbmmon bridging member having cylindrical plugs refleived in the open ends of the hollow rods and rigidly secured thereto by weldmerits. Such known heating elements are especially adapted for use in the prod-notion of float glass wherein -'a large number of these elements, on the order of from 600 to 1,500 elements for example, are vertically SuS-- pended from the roofof a large furnace above the level of the molten material'on' which the flat glass product floats. In mounting each of these known elements, the I three rods are fitted in the bores of a frustoconical refractory block disposed in a correspondingly shaped ;-'hole in the top-wall of the furnace.

Such known silicon carbide heating elements have not been entirely' satisfactory becauseof the weakness s j'jinherent at the weldments between the rods and the 'yibrid'ging'member and which are subjected to stresses induced therein during the heating thereof. The fstressesgenerated at the weldmentscause premature gf failure. ofthe heating element. Also, the peculiar and -awkward shape of these known fragile elements ren-' ders them susceptible to breakage during handling and shipping; Furthermore, in replacingone or more spent a 'elem'ent's, thespecially configurated refractoryblocks mustbe removed or the elements inserted from within 3 the furnace, which is not feasible while the furnace'is I in operation. The tendency for the refractory blocks to adhere to the furnace walls alsocornpounds the prob- ,lemsfencountered'in element removal and replace- 1 SUMMARY OF THEIINVENTION.

A primary object of the present invention is to pro vide an improved three-phase, silicon carbide. heating scriptionof an illustrative embodiment thereof, taken together with the accompanying drawing wherein like reference numerals denote like parts throughout the various views.

BRIEF DESCRIPTION OF THE DRAWING FIGURES 3-3 of FIG. 1;

FIG. 4 is an elevational view of the end opposite that shown in FIG. 2;

FIG. 5 is a view similar to FIG. 1, showing an insulating filler material deposited in the spiral slots between adjacent convolutions of the spirally configurated hot zone section; and

FIG. 6 is a cross sectional view, taken about on line 6-'6 of- FIG. 5.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT tending axially therethrough.

Resistance body 12 is formed in a unitary, one-piece construction ofa homogeneous mass of very dense, self-bonded or'recrystallized silicon carbidematerial capable of withstanding elevated operating temperatures without disintegration or material deterioration,

is non-corrosive, andwhichchanges in resistance very slightly, slowly and uniformly in use to provide stable heating over a long period of use. vResistance body 12 includes a cold zone terminal section l6'and a hot zone section l8. In forming the 5 equally circumferentiallyspaced slots 20, 22 and 24 are element avoiding't he above noted disadvantages and,

which is formed in a unitary, one-piece construction,

. Another object'of. this invention is to provide an improved silicon carbideheating element of the three;- phase electricalfiresistance type which is strong and rigid in construction, rugged-and durable in us'e com-f pactly and homogenously formed, and which is readily minimum of inconvenience.

operation at 'a' dial wall thickness of resistance body 12, forming concold zone terminal section; 16 in the solid cylindrically shaped wall of resistance. body 12, three elongated,

cut through the radial'wall thickness of body 12 extendingaXiaIIyinWardIy from one end 26 thereof to form three arcuately shaped, circumferentially spaced elongated members or legs 28, 30 and 32.

The hot zone section 18 is similarly formed by cutting three parallel, spiral slots'34, 36 and 38 through theratinuations of slots 20, 22 and.24 and extendingfrom the 1146. These spirals 42, 44 and 46 are connected at their drical body formed of silicon carbide having threeelom gated, laterally spaced legsforming the cold end terminal sectionj and'three parallel. spirals constituting the hot zone section of thefelement-u The spirals extend from the inner ends of the legs in ajhelical path along the body and terminate vin a common end junction. An insulating filler material can be deposited in the slots separating the spirals.

The foregoing and other objects advantages, and characterizing features of the presentjinvention will become clearly apparent from the ensuing detailed detional areas of the former relative to thelatter. Thus,

inner ends thereof toward the opposite end 40 of resisi tance body 12 to form three parallel spirals 42, '44 and inner ends to legs 28, 30 and 32 and are formed integral therewith. Spirals 42-46 extend in a helical path longitudinally of the remaining portion of resistance body 12 and terminate in a common terminal end juncture or Wye connection 48 adjacent the opposite end 40 of resista'nce'body l2.

The resistance of spirals 42, 44 and 46 is significantly greater than the resistance of their associated legs 28,

30 and 32 because of the appreciably smaller cross secwhen power is supplied to heating element 10, the

higher resistance of spirals 42 46 generates high temperatures therein to form the hot zone or effective heating portion of element 10. V The higher resistance offered by the reduced cross sectional areas'of the spirals 42, 44 and 46 enables resistance body 12 to be-form'ed of a very dense silicon carbidematerial without sacrificing resistance capabilities as opposed to the'less dense silicon carbide'materials incorporated in the solid walls of the hollow resistance rods employed in the known heating elements used today. Since an increase in material density generally decreases the resistance of a body, the density of these known elements must necessarily be seriously compromised in obtaining desired resistance capabiliciably increased as opposed to known silicon carbide heating elements, which densities are dictated by resistance design requirements. By way of example, the .density of resistance body 12 of this invention can vary vfrom'about 2.7 to 2.8 grams/cc as contrasted toiknown silicon carbide heating elementswhich have densities ran'gingrfrom about 2.2 to 2.4 grams/cc. The increased density ofthesilicon carbide material forming the heating element 10 of the present invention adds greater stability and strength thereto.

j For additional strength, the spaces defined by spiral slots 34, 36v andj38 between adjacent windings or convolutions'of spirals 42, 44 and 46 can be filled with an impervious, insulating filler material 50, as shown in FlGS'.,-5 and 6. Thiswadded strength offers flexibility in design, enabling'the hot zone portion to be extended and the crossjsec'tiona'l; areas of the spirals 42-46 reduced to' increase resistance, as desired, since the tiller material 50 formswith the spirals 42-46 a continuous undesirablecontaminants therein, which could promote short circuiting or induce stresses in the hot zone spacedrelation and preclude short circuiting therebetween. 1 I

From the foregoing, it is apparent that the present invention accomplishes its intended objects. The provision of a three-phase electrical heating element formed of a unitary, one-piece constructionof a dense, recrystallized silicon carbide avoids stresses otherwise generated in welded multiple rod elements of known construction. The elimination of such stresses in the heating element of this invention minimizes fractures and breakage to prolong the useful, operating life thereof. Also, because the heating element is formed in a compact, rod like configuration, it can be easily handled to decrease the possibilities of damage during handling and shipping. Moreover, the heatingelement of this invention requires only a minimum of supporting structure and can be simply inserted through'a suitable bore in a-furnace wall for ease of installation'and replacement. The'provision of electrical termination .at one end only simplifies the attachment of electrical connections thereto, -further facilitating installation and replacement. Indeed, the heating element of this invention can be efficiently replacedwhile the furnace is op erating, thereby eliminating furnace shutdown time By vfilling th'e spiralslotsfin the heating section with the desired insulating material, a stronger heating element is section l8'to causefjpremature,failure o fheating elementl0. :i Insulating material iscomprised-of a zircon base,

ceramic insulating material provided {with ."a fsuitable binder and has a coeff cient of thermal expansion sub:

stantially similar to that. of silicon carbide to avoid stresses in heating element 10 causedibyithermalvariations. Moreover, such material, which is described and.

claimed. in copending applicationfser. ,No; -39f,8,l85', v7 filed simultaneously herewith, is capableof withstanding the operating temperatures of heating element 1t)v 1- provided and contaminant accumulation is appreciably reduced; f' g I A..preferred embodiment of this invention having been described and illustratedin detail, it should be understood that; this has been done by way of illustration only. l

I claim:

l. A heating element comprisingf anv elongated hollow body formed of a dense,' non-metallic, electrical re-' sistance material; saidbody having a cold zone section and a hot zone section; said coldzone section comprising three laterally spaced elongatedmembers extend ing longitudinally inwardly from one end of said body; each of said elongated members being provided with electrical conducting material to provide electrical terminals for saidhollow body; said hot zonesectioncom- "prising three spaced, parallel spirals connected to' the inner ends'of said elongated members, respectively and extending therefrom in a helical path longitudinally along substantially the remainder of saidbody; said 'spirals terminating in a common end juncture; each of said without decomposing or becoming-electrically conducr tive and remains stable in both reducing and oxidizing A atmospheres over the entire temperaturebperatingj1 range of heating element-10. A coating of any suitable electrical conductingmaterial 5,2, such as aluminum for example, canbe sprayed or otherwise deposited on the outer and inner-surfaces of legs 28, 30 and 32 adjacent end 26 to provide electrical terminalsforresistance body 12. Various electrical contact arrangements, provided with conductors leadspirals having a lesser cross'sectional area-than the elong'atedmember to which it is joined; said spirals being spaced from each other. by spirals slots formed in said body; and a zircon base ceramic insulating filler" material permanently disposed in said slots between saidspirals.preventing accumulation of contaminants} andffor strengthening said element, said filler. material 'havingla coefficient of expansion substantially-similar to the coefficient of expansion of saidelectrical resistance m'a'terial, said filler material remaining in said slots and'being capable of withstanding temperatures over. the entire foperating temperature range of said heating element from room temperature up to about f of a homogeneous mass of said non-metallic, electrical resistance material.

6. A heating element according to claim 1 wherein said electrical resistance material is dense, recrystallized silicon carbide and said body is formed in a unitary one-piece construction of a homogeneous mass of said dense, recrystallized silicon carbide; and a coating of said electrical conducting material deposited on the outer surfaces of said elongated members adjacent said 

1. A heating element comprising: an elongated hollow body formed of a dense, non-metallic, electrical resistance material; said body having a cold zone section and a hot zone section; said cold zone section comprising three laterally spaced elongated members extending longitudinally inwardly from one end of said body; each of said elongated members being provided with electrical conducting material to provide electrical terminals for said hollow body; said hot zone section comprising three spaced, parallel spirals connected to the inner ends of said elongated members, respectively, and extending therefrom in a helical path longitudinally along substantially the remainder of said body; said spirals terminating in a common end juncture; each of said spirals having a lesser cross sectional area than the elongated member to which it is joined; said spirals being spaced from each other by spirals slots formed in said body; and a zircon base ceramic insulating filler material permanently disposed in said slots between said spirals preventing accumulation of contaminants and for strengthening said element, said filler material having a coefficient of expansion substantially similar to the coefficient of expansion of said electrical resistance material, said filler material remaining in said slots and being capable of withstanding temperatures over the entire operating temperature range of said heating element from room temperature up to about 3,100*F.
 2. A heating element according to claim 1 wherein said body is formed in a unitary one-piece construction of a homogeneous mass of said non-metallic, electrical resistance material.
 3. A heating element according to claim 1 wherein said electrical resistance material is dense, recrystallized silicon carbide.
 4. A heating element according to claim 2 wherein said electrical resistance material is dense, recrystallized silicon carbide.
 5. A heating element according to claim 1 including a coating of said electrical conducting material deposited on the outer surfaces of said elongated members adjacent said one end of said body.
 6. A heating element according to claim 1 wherein said electrical resistance material is dense, recrystallized silicon carbide and said body is formed in a unitary one-piece construction of a homogeneous mass of said dense, recrystallized silicon carbide; and a coating of said electrical conducting material deposited on the outer surfaces of said elongated members adjacent said one end of said body. 